Photoflash lamp

ABSTRACT

A photoflash lamp in which the filamentary combustible material within the lamp envelope comprises a plurality of strands of foil, such as zirconium, each of which have a selected amount of oxide coating on all surfaces of the strand, whereby the lamp exhibits a higher light output and color temperature upon ignition, in addition to changes in timing. The strands of foil are preoxidized by heating in air for a predetermined time at a predetermined temperature.

United States Bouchard et al.

[ Sept. 9, 1975 Primary E.\'aminerCarroll B. Dority, Jr. Attorney, Agent, or FirmEdward J. Coleman 5 7 ABSTRACT A photoflash lamp in which the filamentary combustible material within the lamp envelope comprises a plurality of strands of foil, such as zirconium, each of which have a selected amount of oxide coating on all surfaces of the strand, whereby the lamp exhibits a higher light output and color temperature upon ignition, in addition to changes in timing. The strands of foil are preoxidized by heating in air for a predetermined time at a predetermined temperature.

4 Claims, 2 Drawing Figures PATENTED SEP 9 FIG.2

FIG.I

PHOTOFLASH LAMP This invention relates to photoflash lamps and particularly to fiashlamps containing a filamentary combustible and a method for processing the combustible.

A typical photoflash lamp comprises an hermetically sealed glass envelope, a quantity of combustible material located in the envelope, -and a combustion supporting gas, such as oxygen, at a pressure well above one atmosphere. The lamp also includes an electrically or percussively activated primer for igniting the combustible to flash the lamp.

The combustible material commonly employed in presently available photoflash lamps consists ofa quantity of filamentary material of a type commercially known shredded foil. The material is made by cut ting or shredding a thin sheet or ribbon of suitable metal foil into thin strands. Aluminum and magnesium foil have been used for this purpose, although more recently, zirconium and hafnium have been found to provide significant photomeric advantages.

In the continuing effort to improve light output, higher performance flashlamps have been developed which contain higher combustible fill weights per unit of internal envelope volume, along with higher fill gas pressure, In addition, crimped shred configurations have been employed to further optimize the combustion process. Of course, each of these approaches is limited by physical restraints and consideration of safety.

Accordingly, it is an object of the present invention to provide different means and methods than heretofore employed for attaining further improvements in the light output characteristics of photoflash lamps.

In pursuit of these and other objects, advantages and features, we have discovered. quite unexpectedly that controlled oxidation of all exposed surfaces of a filamentary combustible material, such as shredded zirconium or hafnium foil, can produce significant gains in the light output and color temperature of photoflash lamps. For example, by the use of zirconium shreds preoxidized in accordance with the invention, electrical flash lamps of the type used in commercially available flashcubes have exhibited a light output increase in the order of 3-771 (()25 msec.) and l0l57z (0). Further we have found color temperature improvements in the order of 75K to 200K upon firing individual wads of zirconium shreds in a combustion chamber.

In previous work by Desaulnicrs (See U.S. Pat. No. 3.1 14,250 assigned to the present assignee') it was shown that ultrathin films of zirconium oxide could be deposited on 4" X 4 sheets of zirconium by an anodizing process. These films, obtained on annealed and unannealed zirconium, increased the peak and peak duration as we have similarly observed. However, as described by Desaulnicrs. no important differences in total light output were noted". Hence. although timing changes are predictable from the Desaulnicrs patent, the gains in light output and color temperature which we have observed using our preoxidized shreds were totally unexpected.

The anodizing method described by Desaulnicrs posed several problems. The necessity for nitric acid baths; rejuvenation and disposal of acid solution; power requirements for depositions; rinsing and drying of the anodized foil do not lend themseleves to economical high speed production processing. Further disadvantages include the difficulty of anodizing foils on a continuous basis, as well as the ability to anodize only two exposed foil surfaces. The latter disadvantage results in shredded material with only two of the exposed surfaces of each strand being oxidized.

According to our invention, we have found a considerably less difficult process for shred oxidation which can be utilized with improved results. More specifically, we have found that heating 19.5 mgs. of wadded zirconium shreds in air (we used a box furnace) at temperatures from 275C to 600C for periods of 5 to 30 minutes results in-oxide coatings having varying optical and timing characteristics in lamps depending on the degree of oxidation. Generally, the oxidized shreds have surface colors ranging from light straw for the 275C heated samples to grayb1ack for the 600C sam ples. In our experiments we deliberately removed the wads from the flash bottles prior to the sealing operation. Wads were placed in 7 mm I.D. X 25 mm quartz sleeves for sample handling convenience during the oxidation process. The procedure of removing the wads from lamp envelopes is not necessary for the oxidation of shreds, but is only performed to assure that no oxidation of primer materials occurs. Of course, in a production process this oxidation procedure may be performed after shredding and prior to blowing the wads into the lamp envelope. Investigation by instrumental analyses of the surface layer of zirconium foils (repre sentative of shreds) oxidized in air at temperatures of 300C, 400C, 500C and 600C. did not indicate any reaction between nitrogen present in the air firings with the zirconium metal. Nitration of the zirconium should be avoided if possible. The procedure herein described can be altered bysubstitution of pure oxygen for the ambient air atmosphere. Likewise, methods of heating shreds in the lamp envelopes could be used providing the primer is not excessively heated to destroy lamp timing properties.

Referring now to the drawings:

FIG. 1 is an elevational view of an electrically ignitable photoflash lamp containing a preoxidized filamen tary combustible in accordance with the invention; and

FIG. 2 is an enlarged representation of a crosssection of a single strand of the filamentary combustible material in the lamp of FIG. 1. illustrating the oxide coating on all exposed surfaces thereof.

The teachings of the present'invention are applicable to either percussive or electrically ignited photofiash lamps of a wide variety of sizes and shapes; however, the invention is particularly advantageous as applied to llashlamps having tubular shaped envelopes with a volume of less than one cubic centimeter. For purposes of example, the invention will be described as applied to the electrically ignitable photoflash lamps illustrated in FIG. 1.

Referring to FIG. 1, the lamp comprises an hermetically sealed lamp envelope 2 of glass tubing having a press 4 defining one end thereof and an exhaust tip 6 defining the other end thereof. Supported by the press 4 is an ignition means comprising a pair of lead-in wires 8 and 10 extending through and sealed into the press. A filament l2 spans the inner ends of the lead-in wires. and beads of primer l4 and 16 are located on the inner ends of the lead-in wires 8 and 10, respectively, at their junction with the filament. Typicallythe lamp envelope 2 has an internal diameter of less than one-half inch, and an internal volume of less than one cubic centimeter. A combustion-supporting gas, such as oxygen, and

a filamentary combustible material 18, such as shredded zirconium or hafnium foil, are disposed within'the lamp envelope. Typically, the cornbustion-supportirig gas is at a pressure exceeding one atmosphere, with the more recent subminiature lamp types having oxygen fill pressures of up to several atmospheres.

A percussive type photoflash lamp is described in several prior patents of the present assignee; for exanr ple U.S. Pat. No. 3,674.4l 1. As described therein. the percussive lamp also includes a sealed glass envelope containing a filamentary combustible material and a combustion-supporting gas; however, the ignition means comprises a metal primer tube sealed in and depending from one end of the glass envelope and containing a coaxially disposed wire anvil partially coated with a charge of fulminating material. A deflectorshield is located on the wire anvil just above the inner .mouth of the primer tube.

Although somewhat different in structure and operation, the electrical and percussive lamps are similar in that in each the ignition means is attached to one end of the lamp envelope and disposed in operative relationship with respect to the filamentary combustible material. More specifically, the igniter filament 12 of the flash lamp in FIG. 1 is incandesced electrically by current passing through the metal filament support leads 8 and 10. whereupon the incandesced filament ignites the beads of primer l4 and 16 which in turn ignite the combustible 18 disposed within the lamp envelope. Operation of the percussive-type lamp is initiated by an impact onto the primer tube to cause deflagration of the fulminating material up through the tube to ignite the combustible disposed within the lamp envelope.

As previously mentioned, the filamentary combustible material employed in flash lamp envelopes normally comprises a shredded metallic foil, such as zirconium or hafnium. The metallic foil manufactured for this application is normally provided in thickness of about or somewhat less than one mil and in widths of about four inches. The foil is then processed through standard shredding equipment to produce desirable cross-sections of about 1.0 to 2.0 square mils. depending upon the characteristics of various photoflash lamps. Accordingly. the strands of shredded foil in photoflash lamps are normally about four inches long. although there are many applications in which the foil is split to provide much shorter strand lengths for the filamentary combustible.

In accordance with the present invention. the shredded metal foil forming the filamentary combustible material 18 is oxidized by controlled heating in air or oxygen. as described hereinbefore. This preoxidation of the shreds of combustible foil results in an oxide coating 20 on all surfaces of each strand of metal foil 22, as illustrated in FIG. 2. For example, if the metal foil 22 is zirconium. our controlled preoxidation process will result in the formation of a selected amount of Zirconium oxide 20 on all four surfaces of the strand. as viewed in cross-section.

We have indicated that use of the abovedescribed preoxidized shreds. or strands. of filamentary combustible material provides improved light output and color temperature in addition to increased peak time. Actual comparative measurements conducted on 19.5 mg. wads of preoxidized versus nonoxidized shreds of Zirconium foil in a combustion chamber containing oxygen at 12 atmospheres pressure resulted in the following sets of averaged data for each condition of oxidation.

These data substantiate that a continuing increase in color temperature, peak time. and half time duration is obtainable with increased amounts of oxidation on the shredded strands, as determined by increased temperatures during the preoxidation process. The data also show a nearly 571 increase in the average light output of the 300C oxidized samples as compared to the control samples; a slight increase for the 500C samples;

and a slight decrease. or leveling off. for the 600C samples. As would be expected, the peak light intensity decreases with increased oxidation. The leveling off of average light intensity at 600C indicates a maximum limit at which increased amounts of oxidation are beneficial to the average light output.

The luminosity output gains are even more surprising when viewed in the light that less zirconium is available for combustion. For instance. we have determined from weight measurements that 300C oxidized samples have only 97.1% as mcuh available metal for combustion as non-oxidized samples (as denoted in the data table above). This would inidcate that for equal weights of metal available for combustion. pre-oxidized shreds should yield even greater quantities of light. Viewed in another fashion, one would expect need for less oxygen in lamps containing pre-oxidized shreds. thus lowering lamp pressures and increasing lamp containment reliabilities.

The optical effects of varying amounts of shred preoxidation were also tested in photoflash lamps of the type employed in commercially available flash cubes with similar results obtaining. For example. the following is a summary of the averaged data measured for electrical tlashlamps having a tubular glass envelope having an outside diameter of 0.350 inch, an inside diameter of 0.293 inch and a volume of().o8 cubic centimeter. The envelope contained approximately 19 mgs. of shredded zirconium foil and oxygen at a'pressure of 500 cm. Hg. The oxidized shreds were heated in air for 15 minutes at the various temperatures indi cated.

Peak" Output Output Peak Height U-15nisec. 'l otal Rise Decay 'l'imu i'mcga- (lumcn- (lumcir lime 'l ime Description (msec.) lunicnsl sec sec.) (nisec. (niscc.

Zr Shrcds ('ontrol $.l .303 417i! 482. 5,2 IN. Zr Shrcds ()xitli/ed 275C *1. I .336 4237 5222 o i) 20.4 Zr Shrcds ()\idi/cd 425% lo.4 ,Rni 4352 53% (\.S 1 n '/.r Shrcds (Midi/ed (\(JUC 151i .24) 3071 4234 lll,7 l

The light output of the lamps containing shreds oxidizcd at 425C shows an increase of over 4% (()25msec.) and approximately lIZVr ((l- In the case of shreds oxidized at 600C, however, a sharp drop in light output was observed, again indicating a maximum limitation on the amount of oxidation. The value of peak height for lamps containing shreds oxidized at 425C is observed to be somewhat askew for reasons we have not determined.

In summary, whereas the aforementioned Desaulni ers patent does not indicate any significant gains in light output or color temperature resulting from anodized foil, we find a gain using shreds controllably oxidized in the manner we have described. We believe the reason may lie in the fact that all exposed surfaces of the strands of foil are oxidized in our case, whereas only two surface of each strand of foil were oxidized by the Desaulniers anodizing process. Further, impurities were probably introduced upon the surface of the foil during the anodizing process which negated for Desaulniers the gains we have observed with our preoxidized shreds.

Although the invention has been described with respect to specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention. Other combustible materials may be used. For example, we feel that the filamentary material for preoxidation should comprise a combustible which burns at the surface of a molten globule by oxygen diffusion through an oxide coating thereon, such as zirconium, hafnium, thorium, yttrium, or combinations thereof. rather than a combustible which burns as a vapor, such as magnesium or aluminum.

What we claim is:

l. A photoflash lamp comprising:

an hermetically sealed, light-transmitting envelope;

at combustion-supporting gas in said envelope;

a quantity of filamentary combustible material located within said envelope, said filamentary material comprising a plurality of strands each having an oxide coating which entirely covers all surfaces thereof. whereby said lamp exhibits a higher light output and color temperature upon ignition of said oxidized filamentary material than a like lamp containing a filamentary combustible material which has not been preoxidizcd. said light output increase being at least about 3% (025 msec.) and l0)? (0 and ignition means attached to one end of said envelope and disposed in operative relationship with respect to said combustible material.

2. A lamp according to claim 1 wherein said filamentary material comprises a combustible which when ignited burns at the surface of a molten glouble by oxygen diffusion through an oxide coating thereon.

3. A lamp according to claim 2 wherein the material comprising said filamentary combustible is selected from the group consisting of zirconium, hafnium. thorium, yttrium. and combinations thereof.

4. A lamp according to claim 1 wherein each of said strands of filamentary combustible material has a selected amount of oxidation which entirely covers all surfaces thereof. 

1. A PHOTOFLASH LAMP COMPRISING: AN HERMETICALLY SEALED, LIGHT-TRANSMITTING ENVELOPE, A COMBUSTION-SUPPORTING GAS IN SAID ENVELOPE, A QUANTITY OF FILAMENTARY COMBUSTIBLE MATERIAL LOCATED WITHIN SAID ENVELOPE, SAID FILAMENTARY MATERIAL COMPRISING A PLURALITY OF STRANDS EACH HAVING AN OXIDE COATING WHICH ENTIRELY COVERS ALL SURFACE THEREOF, WHEREBY SAID LAMP EXHIBITS A HIGHER LIGHT OUTPUT AND COLOR TEMPERATURE UPON IGNITION OF SAID OXIDIZED FILAMENTARY MATERIAL THAN A LIKE LAMP CONTAINING A FILAMENTARY COMBUSTIBLE MATERIAL WHICH HAS NOT BEEN PREOXIDIZED, SAID LIGHT OUTPUT INCREASE BEING AT LEAST ABOUT 3% (0-25MSEC.) AND 10% 70-$), AND IGNITION MEANS ATTACHED TO ONE END OF SAID ENVELOPE AND DISPOSED IN OPERATIVE RELATIONSHIP WITH RESPECT TO SAID COMBUSTIBLE MATERIAL.
 2. A lamp according to claim 1 wherein said filamentary material comprises a combustible which when ignited burns at the surface of a molten glouble by oxygen diffusion through an oxide coating thereon.
 3. A lamp according to claim 2 wherein the material comprising said filamentary combustible is selected from the group consisting of zirconium, hafnium, thorium, yttrium, and combinations thereof.
 4. A lamp according to claim 1 wherein each of said strands of filamentary combustible material has a selected amount of oxidation which entirely covers all surfaces thereof. 